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£j*ix«»J STATES DEPARTMENT OF AGRICULTURE 

€■1 BULLETIN No. 507 C 



S^^-^mfU 



n from the States Relation Service 
A. C. TRUE, Director. 




*&\J7' < >^rU 



Washington, D. C. 



PROFESSIONAL PAPER 



March 24, 1917 



STUDIES ON THE DIGESTIBILITY OF SOME 
ANIMAL FATS. 

By C. F. Langworthy, C/«'e/, and A. D. Holmes, Scientific Assistant, Office of Home 

Economics. 



CONTENTS. 



Introduction 

Experimental methods. 



Page. 
1 

2 



Page. 

Digestion experiments— Chicken fat, goose 
fat, brisket fat, cream, and fat in egg yolk 
and in fish 4 

Summary IS 



INTRODUCTION. 

Previous papers * reported the results of experiments undertaken 
to determine the thoroughness of digestion of lard, beef fat, mutton 
fat, butter, olive oil, cottonseed oil, peanut oil, coconut oil, sesame 
oil, and cocoa butter, which showed that fairly large quantities of 
these fats incorporated in a simple mixed diet could be eaten without 
digestive disturbances and that all were well digested, the coefficient 
of digestibility being proportional to the melting point of the fat. 
In continuation of the study of annual and vegetable fats and their 
dietetic uses, this bulletin reports a study of the digestibility of 
chicken fat, goose fat, brisket fat, cream, fat in egg yolk, and fat 
or oil in fish. 

Fats are so very similar in their chemical nature that it is natural 
to assume that they would not differ materially with respect to their 
food value (of which digestibility is an important factor) under 
comparable conditions. While race experience would indicate that 
this is true in the main, there is reason to believe that the question 
of the digestibility of fats and the closely related matter of the 
energy which they supply to the body merit further study. That 
the digestion of different sorts is not alike in all its steps is indicated 

i TJ. S. Dept. Agr. Buls. 310 (1915); 505 (1917). 
Note.— This bulletin records studies of the digestibility of chicken fat, goose fat, brisket fat, cream, fat 
in egg yolk, and fat or oil in fish. It is primarily of interest to students and investigators of food problems. 
70239°— Bull. 507—17 1 



Monograph j 






&«.< 



2 BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. -£Ol ^ 

by the work of Tangl and Erdelyi * and of Yon Fejer, 2 who have 
observed that fats with a melting point somewhat higher than 
normal body temperature do not leave the stomach so readily as 
those of a lower melting point, and, furthermore, that they are not 
so easily emulsified in the intestine. Apparently no connection has 
been shown between these observations and thoroughness of diges- 
tion. Before one can assume that the fuel value of fat, or more 
accurately the fuel value of digested fat, actually represents its 
energy value to the body, one must take into account such work as 
that of Lusk 3 and his associates, which showed that the digestion 
and assimilation of foods (including fat) caused an increased output 
of energy, not ascribable to muscular work, and designated specific- 
dynamic effect. The test reported did not compare different fats. 

That in comparing fats we must consider not alone such questions 
of thoroughness of digestion and energy expenditure as a result of 
digestion and their relation to nutrition is apparent from recent work 
of McCollum and Davis 4 and Osborne and Mendel, 5 who concluded 
that certain fats carry either as an .integral part or as a complement 
a small amount of substance important in growth. In discussing 
dietetics, it is commonly assumed that fat and carbohydrates can 
replace each other as sources of energy in proportion to their theo- 
retical energy values. There are times when it is not wise to do 
this, at least under pathological conditions, as recent work would 
indicate, since, according to Ringer, 6 there is a limit beyond which 
this replacement can not go without serious results, some carbohy- 
drate, it is claimed, being essential .for the complete combustion of fat, 

EXPERIMENTAL METHODS. 

The investigations here reported form a part of a series of studies 
of the thoroughness of digestion of culinary and table fats of animal 
and vegetable origin, including those eaten as such, those added to 
foods in cookery, and those which form an integral part of the foods 
in which they naturally occur. In all the same general procedure 
was followed. 

The experimental methods were those adopted in earlier work 7 
carried on by the department as a part of its investigations of the 
nutritive value of foods as a result of extended studies of the advan- 
tages and disadvantages of differences in technique and in laboratory 
methods. 

The subjects were young men (medical or dental students) in 
good health, of similar occupation and muscular activity. The diets 

i Biochem. Ztschr., 34 (1911), No. 1-2, pp. 94-lin. 

2 Idem, 53 (1913), No. 1-2, pp. 168-178. 

s Jour. Biol. Chem., 22 (1915), No. 1, pp. 15-41; Cornell Univ. Med. Bill., 5 (1915), No. 2 (pt. 1, paper 14). 

« Jour. Biol. Chem., 15 (1913), No. 1, pp. 167-175. 

& Idem, 16 (1913), No. 3, pp. 423^37; 17 (1914), No. 3, pp. 401-408. 

6 Idem, 17 (1914), No. 2, pp. 107-119. 

i U. S. Dept. Agr., Office Expt.'Stas. Bui. 143 (1904$, pp. 57-77. 

D a of D. 
APR J3 1917 



DIGESTIBILITY OF SOME ANIMAL FATS. 3 

were simple, the fat-containing food, which was the principal item, 
being supplemented in each case by carbohydrate foods (such as 
biscuits or crackers, and mashed potato), fruit (oranges or apples), 
and tea or coffee with sugar, if a beverage besides water was desired. 
The subjects were not required to eat like quantities of the food 
supplying the fat, or of the other foods, but in every case they were 
expected to eat an amount of fat which would supply about 30 
per cent of the total energy value of the ration, this being the quan- 
tity which fat contributes to the average American and European 
diet, as shown by a compilation of data made for this study. With 
the experimental diets chosen this would mean about 100 grams of 
fat. Special pains were always taken to use fat which was not 
rancid, since Adler, 1 on the basis of experimental data, has attributed 
a hemolytic action to the presence of free fatty acids in foods. 

In making up the diets for the experiments a stiff cornstarch pud- 
ding or blancmange (heavily flavored with caramel to mask any 
distinctive fat flavor) was used as a vehicle for the separated fats. 
The same sort of blancmange was also used in the experiments with 
cream and egg yolk. For the study of fish oil a typical fat fish was 
used as the source of the fat. 

In these, as in the earlier digestion experiments reported, the three- 
day or nine-meal test period proved entirely satisfactory. The test 
periods were followed by rest periods of four days, in which the sub- 
jects were permitted to eat whatever they desired. Obviously, the 
diet during the experimental periods was limited to the prescribed 
ration. In every case weighed portions of the different foods were 
prepared in advance for each meal for each subject and the subjects 
were instructed to reserve any uneaten portions of the diet for weigh- 
ing, in order that the exact amount eaten might be ascertained. 
They were also instructed to observe due care in the collection and 
separation of the feces pertaining to an experimental period. 

The records of the experiments include data for the amounts of 
food eaten and for the feces. Samples of both food and feces were 
analyzed to determine what percentages of protein and carbohydrate 
as well as fat were available to the body. 

The percentage of fat in the feces was determined by ether extrac- 
tion of the air-dried sample for 18 to 20 hours by the Soxhlet method, 
as described by the Association of Official Agricultural Chemists. 2 
It is recognized that by this method some fat in the form of soaps 
may not be extracted. However, comparative tests by the Folin- 
Wentworth 3 method and the Soxhlet method, made as a part of the 
digestion work of this office, have given results that are not uniform 
and are not significant from the standpoint of dietetics. 

The ether extract obtained by the method followed is assumed to 
represent the fat of undigested food, and this quantity less the pro- 

i Jour. Med. Research, 2S (1913), No. 1, pp. 199-226. 2 U. S. Dept. Agr.. Bur. Chem. Bui. 107 (1912). 
'■> Jour. Biol. Chem., 7 (1910), No. 6, pp. 424, 42f, 



4 BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. 

portion ascribable to the fat supplied by the basal ration to repre- 
sent the undigested portion of the fat studied. The significance of 
such values, in discussing problems of dietetics and the theoretical 
and other considerations having to do with metabolic products in 
feces, are fully discussed in earlier publications. 1 

DIGESTION EXPERIMENTS. 

CHICKEN FAT. 

Although chicken fat as such is not available in quantity in most 
markets the very large demand for poultry, especially mature poultry, 
would indicate a very considerable consumption of the fat along with 
the chicken meat. Little information, however, as to its digestibility 
and nutritive value has been found in a survey of the literature. In 
studies of the digestibility of fish and poultry, Milner 2 found that 
chicken fat eaten as an integral part of poultry in a simple mixed diet 
was 97 per cent digested. 

Several pounds of chicken fat, which had been taken in small quan- 
tities from fat birds drawn at the market for those not desiring the 
excess fat, were procured. It was passed through an ordinary meat 
grinder and heated in a double boiler to a temperature higher than 
its melting point, after which the fat was easily separated from sur- 
rounding tissues by straining. 

For use in the digestion experiments the product was thorough^ 
mixed and incorporated in a blancmange or cornstarch pudding in 
the way previously described. Eight experiments of three days' 
duration were completed in which four normal subjects assisted. 
The results of these tests are recorded in the following tables: 
Data of digestion experiments with chicken jut in a simple mixed diet. 





Weight. 

Grains. 
2, 357. 

545.0 
1,549.0 

192.0 


Water. 


Pro- 
tein. 


Fat. 


Carbo- 
hydrates. 


Ash. 


Experiment No. 274, subject H. F. B.: 


Gra ms. 

1,072.0 

49.0 

1,346.1 


Grams. 
45.7 
57.8 
12.4 


Grams. 

359.7 

8.2 

3.1 


Grams. 
863.6 
421.3 
179.7 
192.0 


Grams. 
16 




8.7 


Fruit 


7.7 
















Total food consumed 


4,643.0 
148.0 


2, 467. 1 


115.9 
44.4 
71.5 


371.0 

26.4 

344.6 


1,656.6 

65.0 

1,591.6 


32.4 




12 2 






20 2 












61.7 


92.9 


96.1 


62 3 








Experiment No. 275, subject D. G. G.: 


1, 597. 
396.0 
492.0 
158.0 


726.3 
35.7 
427. 5 


31.0 
42.0 
3.9 


243.7 
5.9 
1.0 


585.1 
306.1 
57.1 
158.0 


10 9 




6 3 


Fruit 


2 5 














Total food consumed 


2,643.0 
88.0 


1,189.5 


76.9 
26.2 

50.7 


250.6 

15.6 

235.0 


1, 106. 3 

40.1 

1,066.2 


19 7 




6 1 






13 6 












65.9 


93.8 


96.4 


69 










i U. S. Dept. Agr., Office Expt. Stas. Buls 126 (1903), pp. 18-20; 193 (1907), pp. 47-59; Connecticut Storrs 
Sta. Rpt. 1896. pp. 178-180. 
2 Connecticut Storrs Sta. Rpt. 1905, pp. 135, 136. 



DIGESTIBILITY OF SOME ANIMAL FATS. 5 

Data of digestion experiments with chicken fat in a simple mixed diet — Continued. 





Weight. 


Water. 


Pro- 
tein. 


Fat. 


Carbo- 
hydrates. 


Ash. 


Experiment No. 276, subject R. L. S.: 


Grams. 

2,073.0 
340.0 
946.0 
43.0 


Grams. 

942.8 

30.6 

822.1 


Grams. 
40.2 | 
36.0 
7.6 

" 


Grams. 

316.3 
5.1 
1.9 


Grams. 
759.6 
21 12. 8 
109.7 
43.0 


Grams. 
14.1 




5.5 


Fruit 


4.7 














3, 402. 
68.0 


1,795.5 


83.8 1 

20.7 

63.1 


323.3 
17.5 

305.8 


1, 175. 1 

24.0 

1,151.1 


24.3 




5. S 






IS. 5 
















75.3 


94.6 


98.0 


76.1 










Experiment No. 277, subject 0. E. S.: 


2, 380. 
450.0 

1,505.0 
171.0 


1,082.4 

40.5 

1,307.9 


46.2 
47.7 
12.0 


363.2 
6.7 
3.0 


872.0 
347.9 
174.6 
171.0 


16.2 




7.2 


Fruit 


7.5 


















4,506.0 
124.0 


2,430.8 


10.5. 9 
36.7 
69.2 


372.9 
29.9 
343.0 


1,565.5 

46.3 

1,519.2 


30.9 




11. 1 






19.8 
















65.3 


92.0 


97.0 


64.1 










Experiment No. 290, subject H. F. B.: 


1,983.0 

499.0 

1,319.0 

127.0 


903.7 

44.9 

1, 146. 2 


37.2 
52.9 
10.6 


299.4 
7.5 
2.6 


726.2 
385.7 
153.0 
127.0 


16.5 




8.0 


Fruit 


6.6 
















3,928.0 
130. 


2. 094. 8 


100.7 
37.6 
63.1 


309.5 

23.9 

285. 6 


1,391.9 

55.4 

1,336.5 


31.1 




13.1 






. 18.0 
















62.7 


92.3 


96.0 


57.9 










Experiment No. 291, subject D. G. G.: 


1,250.0 
480.0 
636.0 
156.0 


569.6 

43.2 

552.7 


23.5 

50.9 

5.1 


188.7 
7.2 
1.2 


457.8 

371.0 

73.8 

156.0 


10.4 




7 7 


Fruit 


3.2 


















2, 522. 
77.0 


1,165.5 


79.5 
23.9 
55.6 


197.1 
12.0 
185.1 


1,058.6 

32.0 

1,026.6 


21.3 




9.1 






12.2 
















69.9 


93.9 


97.0 


57.3 










Experiment No. 292, subject R. L. S.: 


1,706.0 
413. 
646.0 
54.0 


777.4 
37.2 
561.4 


32.1 

4:>s 
5.2 


257. 6 
6.2 
1.3 


624.7 

319.2 

74.9 

54.0 


14.2 




6.6 


Fruit 


3.2 


















2,819.0 
66.0 


1,376.0 


81.1 
19.5 
61. 6 


265. 1 

12.4 

252.7 


1,072.8 

27.3 

1,045.5 


24.0 




6. S 






17.2 








76.0 


95.3 


97.5 


71.7 


Experiment No. 293, subject 0. E. S.: 


1,708.0 
411.0 

1,273.0 
171.0 


778.3 

37.0 

1, 106. 2 


32.1 
43.6 
10.2 


257.9 
6.1 
2.5 


625.5 
317.7 
147.7 
171.0 


14 2 




6.6 


Fruit 


6.4 








3, 563. 
89.0 


1,921.5 


85.9 
26.3 
59.6 


266.5 

20.7 

245.8 


1,261.9 

33.1 

1,228.8 


27.2 




8.9 






18.3 








69.4 


92.2 


97.4 


67.3 


Average food consumed per subject per day 


1,167.8 


601.7 


30.4 


9S.2 


428.7 


8.8 



6 BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. 

Summary of digestion experiments with chicken fat in a simple mixed diet. 



Experi- 
ment No. 


Subject. 


Protein. 


Fat. 


Carbohy- 
drates. 


Ash. 


274 


H.F. B 


Per cent. 
61.7 
65.9 
75.3 
65.3 
62.7 
69.9 
76.0 
69.4 


Per cent. 
92.9 
93.8 
94.6 
92.0 
92.3 
93.9 
95.3 
92.2 


Per cent. 
96. 1 
96.4 
98.0 
97.0 
96.0 
97.0 
97.5 
97.4 


Per cent. 
62.3 


275 

276 

277 


D. G.G 

R.L.S 

O.E.S 


69.0 
76.1 
64.1 


290 

291 


H. F. B 

D. G. G 


57.9 
57.3 


292 


R.L. S 


71.7 


293 


O. E. S 


67.3 










68.3 


93.4 


96.9 


65.7 









The average coefficient of digestibility of the total fat eaten during 
these tests was 93.4 per cent. As the ether extract of the feces, how- 
ever, is known to contain metabolic product and undigested fat from 
the basal ration, which though nearly so was not absolutely fat free, 
a correction has been applied in the case of this fat and the others 
studied to determine the average digestibility of total fat consumed. 
Digestion experiments with the basal ration as the only source of fat 
have been reported in connection with the earlier animal fat experi- 
ments, from which it was concluded that 9.89 per cent of the total 
weight of water-free feces is made up of metabolic products and undi- 
gested fat from the food, 1 which latter must have been an insignifi- 
cant quantity, since the total amount in the diet was so small. 
Subtracting the quantity represented by this percentage from the 
total ether extract of the feces, a value is obtained more nearly repre- 
senting the weight of unutilized fat. The corrected value for the 
digestibility of fat then becomes 96.7 per cent. 



GOOSE FAT. 



In the United States goose fat is used as such only to a very limited 
extent and chiefly among those of foreign birth or parentage who 
adhere to special food customs. 

Owing to the impossibility of obtaining goose fat in quantity from 
local dealers, an unusually fat or "stall-fed" goose was purchased. 
It weighed 27.5 pounds, 13 pounds of fat being obtained when the fat 
was cut away from the flesh and rendered in the usual way. The 
goose fat, which at room temperature (about 20° C.) is a soft, pale- 
yellow, granular solid, tended to separate into two layers on stand- 
ing — an upper, oily layer, and a lower, more or less solid layer. By 
using freshly rendered fat, rancidity was avoided, which is likely to 
occur on keeping, perhaps owing to the 0.7 to 3.5 per cent of soluble 
fatty acid which the fat contains. 

As regards previous work with this fat, Arnschink 2 conducted an 
experiment of four days' duration with a dog weighing 8 kilograms, 
in which an average of 50 grams, containing 70 per cent of oleic 

1 l". S. Dept. Agr. Bui. 310 (1915), p. 20. 2 Ztschr. Biol., 8 (1890), pp. 443, 444. 



DIGESTIBILITY OF SOME ANIMAL FATS. 



acid and a relatively large amount of free fatty acids was eaten daily 
and 97.51 per cent digested. So far as can be ascertained, no experi- 
ments with human subjects have been recorded. In the work here 
reported a series of seven digestion experiments has been completed, 
the essential data of which are given below. 

Data of digestion experiments with goose fat in a simple mixed diet. 





Weight. 


Water. 


Pro- 
tein. 


Fat. 


Carbo- 
hydrates. 


Ash. 


Experiment No. 209, subject 0. E. S.: 


Grams. 
1,993.0 

162.0 
1, 735. 

206.0 


Grams. 

940.7 

14.6 

1,507.7 


Grom«. 
36. 7 
17.2 
13.9 


Grams. 

212.2 

2.4 

3.5 


Grams. 
789.2 
125.2 
201.2 
206.0 


Grams. 
14.2 




2.6 


Fruit 


8.7 
















Total food consumed 


4,096.0 
71.0 .. 


2, 463. 


67.8 
18.6 
49.2 


218.1 

9.7 

208.4 


1,321.6 

36.9 

1.284. 7 


25. 5 


Feces 


5.8 


Amount utilized 






19.7 
















72. (i 


95. ti 


97.2 


77.3 










Experiment No. 2P2, subject F. F. B.: 


2,424.0 
602. 

1,178.0 
173.0 


1,100.3 

54.2 

1,023.7 


44.6 

63. S 

9.4 


312.9 
9.0 
2.4 


947.8 
465.4 
136.6 
173.0 


18.4 




9.6 


Fruit 


5.9 


















4,377.0 
153.0 


2, 17S. 2 


117.8 
39.7 

78.1 


324.3 
21.5 
302.8 


1,722.8 

80.4 

1,642.4 


33.9 




11.4 






22.5 












1 


66.3 


93.4 


95. 3 


66.4 








Experiment No. 264. subject B. L. S.: 


2,059.0 

321.0 

897.0 

72.0 


934.6 
28.9 
779.5 


37.9 

34.0 

7.2 


265.8 

4.8 
1.8 


805.1 

248. 1 

104.0 

72.0 


15.6 




5.2 


Fruit 


4.5 


















3,349.0 
70.0 


1,743.0 


79.1 
22.6 
56. 5 


272.4 
9.6 

262. 8 


1,229.2 

31.9 

1,197.3 


25.3 




5.9 






19.4 














71.4 


96.5 


97.4 


76.7 










Experiment No. 265, subject 0. E. S. : 


2,451.0 
370.0 

1,219.0 
127.0 


1, 112. 5 

33.3 

1,059.3 


45.1 
39.2 
9.8 


316.4 
5.6 
2.4 


958.4 
2S6.0 
141.4 
127.0 


18.6 




5.9 


Fruit 


6.L 


















4,167.0 
108.0 


2, 205. 1 


94.1 
30.9 
63.2 


324.4 

17.5 

306.9 


1,512.8 

51.8 

1,461.0 


30.6 




7.8 






22.8 














07.2 


94.6 


96.6 


74.5 








Experiment No. 282, subject H. F. B.: 


2,357.0 
501.0 

1,406.0 
165. 


1,118.4 

45.1 

1,221.8 


47.1 
53.1 
11.3 


356. 6 
7.5 
2.8 


822.4 
387.3 
163.1 
165.0 


12.5 




8.0 


Fruit 


7.0 


















4,429.0 
129.0 


2, 385. 3 


111.5 
34.3 

77.3 


366. 9 

16.1 

350.8 


1,537.8 

68.7 

1,469.1 


27.5 




9.9 






17.6 










1 


69.2 


95.6 


95.5 


64.0 








Experiment No. 284, subject B . L. S. : 


1,469.0 

357.0 

452.0 

65.0 


697.0 
32.1 
392.8 


29.4 

37.8 

3.6 


222.3 
5.4 
0. 9 


512. 5 
276.0 
52.4 

65.0 


7.8 




5.7 




2.3 


















2,343.0 
83.0 


1,121.9 


70.8 
26.8 
44.0 


22S. 6 

17. 7 

210.9 


905. 9 

29. 7 
876.2 


15.8 




8.8 






7.0 












62. 1 


92.3 


96. 7 


44.3 









8 BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. 

Data of digestion experiments with goose fat in a simple mixed diet — Continued. 





Weight. 


Water. 


Pro- 
tein. 


Fat. 


Carbo- 
hydrates. 


Ash. 


Experiment No. 2S5, subject 0. E. S.: 


Grams. 
1,977.0 

405.0 
1,083.0 

174.0 


Grams. 
938.1 
36.4 
941.1 


Grams. 
39.5 
42.9 

8.7 


Grams. 

299.1 

6.1 

2.2 


Grams. 
689. 8 
313.1 
125.6 
174.0 


Grams. 
10.5 




6.5 


Fruit 


5.4 
















3,639.0 
99.0 


1,915.6 


91.1 
26.5 
64.6 


307.4 
25.9 
2S1. 5 


1,302.5 

38.9 

1,263.-6 


22. 4 




7.7 






14. 7 
















70.9 


91.6 


97.0 


65. t» 










Average food consumed per subject per day 


1,257.1 


667.3 


30.1 


97.2 


453.9 


8.6 



Summary of digest inn experiments irith goose fat in a simple mixed diet. 



Experi- 
ment No. 


Subject. 


Protein. 


Fat. 


Carbohy- 
drates." 


Ash. 


209 


O. E.S 


Per cent. 
72.6 
66.3 
71.4 
67.2 
69.2 
62.1 
70.9 


Per cent. 
95.6 
93.4 
96.5 
94.6 
95.6 
92.3 
91.6 


Per cent. 
97.2 
95.3 
97.4 
96.6 
95.5 
96.7 
97.0 


Per cent. 
77.3 


262 

264 

265 

282 


H. F.B.... 

R. L. S 

O.E.S. ... 
H. F. B 








66.4 
76.7 
74.5 
64.0 


284 

285 


R.L.S.... 
O.E.S.... 








44. J 
65.6 




Avera 




68.5 


94.2 


96.5 


67.0 









The average coefficient of digestibility of the fat of the ration, of 
which over 97 per cent was goose fat, was 94.2 per cent, while 68.5 per 
cent of the protein and 96.5 per cent of the carbohydrate were 
retained in the body. Making allowance for the metabolic products 
and undigested fat (if any) from the basal ration occurring in the 
ether extract of the feces, the digestibility of goose fat becomes 
95.2 per cent. In practically all the tests the subjects reported 
that the diet had a somewhat laxative effect; in fact, in two or three 
instances this was so pronounced that it was impossible to complete 
the test period and to secure the required experimental data. 
Since an average amount of 95 grams of goose fat was eaten daily, 
however, without any very pronounced physiological disturbances, 
it is reasonable to assume that goose fat in smaller amounts would 
not differ in such respects from other well-known fats, a conclusion 
borne out by the fact that users of the fat in other countries have 
found it not only wholesome but desirable. 

BRISKET FAT. 

In a previous paper x a study of the digestibility of beef kidney 
was reported in comparison with mutton kidney fat and pork kidney 
fat (lard), which showed differences in digestibility corresponding to 
the well-known chemical and physical differences between these fats. 



DIGESTIBILITY OF SOME ANIMAL FATS. 9 

It seemed of interest also to study the digestibility of the fat from 
different parts of the same animal, since these are known to vary 
materially in composition, hardness, culinary qualities, etc. In a 
series of feeding experiments to determine the best ration to use for 
producing firm rather than soft pork, Shutt * found that the com- 
position and physical properties of fat from animals receiving dif- 
ferent rations varied considerably. In some cases the melting 
point of soft bacon was practically 10° C. lower than that of firm 
bacon, and the fat of very young pork was almost always softer than 
that of mature animals. Henriques and Hansen 2 investigated the 
properties of the outer layer of fat in an animal as compared with 
that in the interior of the same animal body, reporting that the 
inner and outer layers of fat are characterized by different iodin 
numbers and solidification points. In similar studies reported by 
Richardson, 3 the melting points of samples of leaf lard from oily hogs 
averaged several degrees higher than the back fat. Richardson and 
Farey 4 later found that the melting points of samples of back fat, 
leaf lard, and ham fat varied as much as 12° to 22° C. 

While the fat of beef animals may not exhibit as wide a variation 
in physical characteristics as occurs in other animals, it is well known 
that brisket fat is quite different from kidney fat. It is softer and 
has a somewhat granular appearance and has some special culinary 
uses. Inasmuch as this variation in characteristics exists, it has 
seemed desirable to test whether there may be a corresponding dif- 
ference in availability to the body. Accordingly, experiments were 
undertaken in which the digestibility of brisket fat was studied under 
conditions identical with those maintained in the study of beef 
kidney fat. 

The material used for this purpose was purchased in the open 
market, separated from the connective tissues of the brisket by the 
method of rendering previously described, and incorporated in the 
blancmange which formed a part of the simple mixed diet used in 
the digestion experiments.' The results of these experiments are 
tabulated on the following page. 

1 Canada Expt. Farms Rpts. 1899, pp. 151-155; Canada Expt. Farms Bui., 38 (1901). 
2Skand. Arch. Physiol., 11 (1901), No. 3-4, pp. 151-165. 
3 Jour. Amer. Chem. Soc, 26 (1904), No. 4, pp. 372-374. 
* Idem, 30 (1908), No. 7, pp. 1191,1192. 

70239°— Bull. 507—17 2 



10 



BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. 



Data of digestion experiments with brisket fat in a simple mixed diet. 





Weight. 


Water. 


Pro- 
tien. 


Fat. 


Carbo- 
hydrates. 


Ash. 


Experiment No. 338, subject H. F B.: 


Grams. 
1,915.0 

404.0 
1, 705. 

205.0 


Grams. 

817.3 

37.9 

1,481.7 


Grams. 
40.7 
40.4 
13.6 


Grams. 

299.1 

5.9 

3.4 


Grams. 
750.0 
313.4 
197.8 
205.0 


Grams. 
7.9 




6.4 


Fruit 


8.5 


















4,229.0 
117.0 


2,336.9 


94.7 
42.0 
52.7 


308.4 

18.2 

290.2 


1,466.2 

44.8 

1,421.4 


22-. 8 




12.0 






10.8 
















55.6 


94.1 


96.9 


47.4 










Experiment No. 339, subject D. G. G.: 


1,611.0 
492.0 

1,326.0 
113.0 


687.6 

46.1 

1,152.3 


34.2 
49.2 
10.6 


251.6 
7.2 

2.7 


631.0 
381.7 
153.8 
113.0 


6.6 




7.8 


Fruit 


6.6 


















3,542.0 
97.0 


1,886.0 


94.0 
33.3 
60.7 


261.5 

14.9 

246.6 


1,279.5 

40.5 

1,239.0 


21.0 




8.3 






12.7 
















64.6 


94.3 


96.8 


60.5 










Experiment No. 340, subject R. L. S.: 


1,845.0 
336.0 

1,318.0 
117.0 


787.4 

31.5 

1,145.3 


39.2 
33.6 
10.6 


288.2 
4.9 
2.6 


722. 6 
260.7 
152.9 
117.0 


7.6 




5.3 


Fruit 


6.6 


















3, 616. 6 
92.0 


1,964.2 


83.4 
27.1 
56.3 


295.7 

12.2 

283.5 


1,253.2 

43.6 

1,209.6 


19.5 




9.1 






10.4 
















67.5 


95.9 


96.5 


53.3 










Experiment No. 341, subject 0. E. S.: 


1,887.0 
364.0 

1,627.0 
338.0 


805.4 

34.1 

1,413.9 


40.1 
36.4 
13..0 


294.8 
5.3 
3.3 


739.0 
282.4 
188.7 
338.0 


7.7 




5.8 


Fruit 


8.1 


















4,216.0 
109.0 


2, 253. 4 


89.5 
36.8 
52.7 


303. 4 

17.3 

286.1 


1,548.1 
44.3 

1,503.8 


21.6 




10.6 






11.0 
















58.9 


94.3 


97.1 


50.9 










Experiment No. 347, subject D. G. G.: 


1,342.0 

388.0 

1,547.0 

92.0 


741.3 

34.9 

1,344.3 


26.9 
41.1 
12.4 


150.3 
5.8 
3.1 


418.0 

300.0 

179.5 

92.0 


5.5 




6.2 


Fruit i • 


7.7 














3,369.0 
121.0 


2, 120. 5 


80.4 
41.0 
39.4 


159.2 

17.4 

141.8 


989.5 

52.0 

937.5 


19.4 




10.6 






8.8 
















49.0 


89.1 


94.7 


45.4 










Experiment No. 348, subject R. L. S.: 


1,509.0 

311.0 

1,440.0 

45.0 


833.6 

28.0 

1,251.4 


30.2 
33.0 
11.5 


169.0 
4.6 
2.9 


470.0 
240.4 
167.0 
45.0 


6.2 




5.0 


Fruit ... 


7.2 
















3,305.0 
83.0 


2,113.0 


74.7 
28.8 
45.9 


176.5 
17.9 
158.6 


922.4 
28.4 
894.0 


18.4 




7.9 






10.5 
















61.4 


89.9 


96.9 


57.1 










Experiment No. 349, subject O. E. S.: 


1,936.0 
289.0 

2,314.0 
259.0 


1,069.5 

26.0 

2,010.9 


38.7 
30.6 
18.5 


216.8 
4.4 
4.6 


603.1 
223.4 
268.4 
259.0 


7.9 




4.6 


Fruit 


11.6 


















4, 798. 
128.0 


3,106.4 


87.8 
42.6 
45.2 


225.8 

17.6 

208.2 


1,353.9 

56.2 

1,297.7 


24.1 




11.6 






12.5 
















51.5 


92.2 


95.8 


51.9 










Average food consumed per subject per day 


1, 289. 3 


751.4 


28.8 


82.4 


419.7 


7.0 



DIGESTIBILITY OF SOME ANIMAL FATS. 11 

Summary of digestion experiments with brisket fat in a simple mixed diet. 



Experiment 
No. 


Subject. 


Protein. 


Fat. 


Carbohy- 
drates. 


Ash. 


338 


H. F. B 


Per cent. 
55.6 
64.6 
67.5 
58.9 
49.0 
61.4 
51.5 


Per cent. 
94.1 
94.3 
95.9 
94.3 
89.1 
89.9 
92 2 


Per cent. 
96.9 
96.8 
96.5 
97.1 
94.7 
96.9 


P,er cent. 


339 


D. G. G 


60.5 
53.3 
50.9 


340 


R.L.S 

0. E.S 


341 


347 


D.G.G 


348 


R.L.S 

O.E.S 


57.1 


349 




Average 








58 4 


92.8 


96.4 













The data of the experiments indicate that the ration supplied 82 
grams of fat daily and that this was 92.8 per cent digested. When 
allowance is made for the small quantity of fat in the basal ration 
and for the metabolic products in the corresponding feces, the digest- 
ibility of brisket fat alone becomes 97.4 per cent. The protein and 
carbohydrate contained hi the diet were 58.4 per cent and 96.4 per 
cent digested,' respectively. 

It is interesting to note that the brisket fat is somewhat more com- 
pletely assimilated than the kidney fat, of which 93 per cent was 
digested, 1 on an average. Although this difference is not very great-, 
it may contribute added evidence to the theory that the properties 
of fats vary with the part of the animal body from which the fats 
are taken. 

CREAM. 

Owing to the pleasant taste and its very general use in the dietary, 
the digestibility of milk fat in the form of cream rather than as a 
separated fat like butter is of particular interest. The question as to 
whether an emulsion or the separated fat is the more thoroughly 
digested has been studied by Wells, 2 who found in the case of cod- 
liver oil that very little difference existed in the digestibility of the 
two forms. In a series of experiments to determine the influence on 
metabolism of an excess of fat in the diet, Atwater 3 found that an 
average of 320 grams of fat daily in a simple mixed diet was 98 per 
cent digested. Approximately 85 per cent of the total quantity of 
fat eaten was furnished by cream and milk. 

The digestibility of butter, as determined in this office in a series of 
eight experiments, was found to be 97 per cent, 4 and in a later series 
of tests, in which the digestibility of the protein of hard palates was 
studied,, butter was found to be 95 per cent digested. 5 Due very 
possibly to the belief that milk fat in all its forms is equally available 
to the body, very few similar studies of cream have been reported. 

i U. S. Dept. Agr. Bui. 310 (1915). 

a Brit. Med. Jour., 2 (1902), No. 2181, pp. 1222-1224. 

a Connecticut Storrs Sta. Rpt. 1901, pp. 230-233. 

4 U. S. Dept. Agr. Bui. 310 (1915), p. 21. 

6 U. S. Dept. Agr., Jour. Agr. Research, 6 (1916), No. 17, pp. 041-648. 



12 



BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. 



A series of experiments, accordingly, has been made to determine the 
digestibility of cream in comparison with that of other fats. 

Cream of average quality was purchased of a local dealer and 
incorporated in a blancmange in the manner previously described, 
except that, owing to the larger volume of the cream, no skim milk 
was necessary and a much smaller amount of cornstarch was needed 
to thicken the mixture. The results of seven digestion experiments, 
in which five different subjects participated, follow: 

Data of digestion experiments with cream in a simple mixed diet. 





Weight. 


Water. 


Pro- 
tein. 


Fat. 


Carbohy- 
drates. 


Ash. 


Experiment No. 180, subject R. L. S.: 


Grams. 
1,461.0 

328.0 

1,116.0 

82.0 


Grams. 

738.8 

29.5 

969.8 


Grams. 

30.5 

34.8 

8.9 


Grams. 

149.2 

4.9 

2.2 


Grams. 

534.3 

253.5 

129.5 

82.0 


Grams. 
8.2 




5.3 


Fruit 


5.6 


















2,987.0 
69.0 


1,738.1 


74.2 
21.7 
52.5 


150. 3 

10.6 

145.7 


999.3 
29.6 
969.7 


19.1 




7.1 






12.0 
















70.8 


93.2 


97.0 


62.8 










Experiment No. 181, subject O. E. S.: 


1,803.0 
145.0 

1,547.0 
197.0 


911.8 

13.0 

1,344.3 


37.7 
15.4 
12.4 


184.1 
2.2 
3.1 


659.3 
112.1 
179.5 
197.0 


10.1 




2.3 


Fruit 


7.7 


















3, 692. 
69.0 


2, 269. 1 


65.5 
18.8 
46.7 


189.4 

11.4 

178.0 


1,147.9 

33.4 

1,114.5 


20.1 




5.4 






14.7 
















71.3 


94.0 


97.1 


73.1 










Experiment No. 182, subject R. F. T.: 


1,885.0 
11.0 

1,580.0 
88.0 


953.2 

1.0 

1,373.0 


39.4 

1.2 

12.6 


192.5 
0.1 
3.2 


689.3 

8.5 

183. 3 

88.0 


10.6 




0.2 


Fruit 


7.9 














3,564.0 
60.0 


2,327.2 


53.2 
12.9 
40.3 


195.8 

14.2 

181.6 


969.1 

26.5 

942.6 


18.7 




6.4 






12.3 
















75.8 


92.7 


97.3 


65.8 










Experiment No. 306, subject II. F. B.: 

Blancmange containing cream 


2, 102. 
523.0 
717.0 
157.0 


1,101.7 

47.1 

623.1 


47.3 

55.4 

5.7 


281.2 
7.8 
1.4 


661.3 

404.3 

83.2 

157.0 


10.5 
8.4 


Fruit 


3.6 












3,499.0 
140.0 


1,771.9 


10S.4 
40.2 
68.2 


290.4 
23.2 

207. 2 


1,305.8 

64.8 

1,241.0 


22.5 




11.8 






10.7 
















62.9 


92.0 


95.0 


47.6 










Experiment No 307, subject D. G G.: 


2,179.0 
485.0 
369.0 
137.0 


1,142.0 

43.6 

320.7 


49.0 

51.4 
3.0 


291.6 
7.3 
0.7 


685.5 
374.9 
42.8 
137.0 


10.9 




7.8 


Fruit 


1.8 










Total food consumed 


3, 170. 
184.0 


1,506.3 


103.4 
59.3 
44.1 


299.6 
32.1 
267.5 


1,240.2 

76.2 

1, 164. 


20.5 


Feces 


16.4 


Amount utilized 




4.1 










Per cent utilized 






43.0 


89.3 


93.9 


12.3 











DIGESTIBILITY OF SOME ANIMAL FATS. 13 

Data of digestion experiments tvith cream, in a simple mixed diet — Continued. 





Weight. 


Water. 


Pro- 
tein. 


Fat. 


Carbohy- 
drates. 


Ash. 


Experiment No. 308, subject R. L. S.: 


Gram,s. 

2,063.0 

330.0 

313.0 

64.0 


Grams. 

1,081.2 

29.7 

272.0 


Grams. 

46. 4 

35. o 

2.5 


Grams. 

276.1 

4.9 

0.6 


Grams. 
649.0 
255.1 
36.3 
64.0 


Grams. 
10. 3 




5.3 


Fruit 


1.6 


















2,770.0 
87.0 


1,382.9 


83.9 
28.7 
55.2 


281.6 
20.4 
261.2 


1,004.4 

28.5 
975.9 


17.2 


Feces 


9. 4 






7.8 










Per cent utilized 






65.8 


92.8 


'.17. 2 


45.3 










Experiment No. 309, subject 0. E. S.: 


2,017.0 
398.0 
767.0 
191.0 


1,057.1 

35.8 

666.5 


45.4 

42.2 

6.1 


269.9 
6.0 
1.5 


634.5 
307.6 
89.0 
191.0 


10. 1 




6.4 


Fruit 


3.9 


















Total food consumed 


3,373.0 
109.0 


1,759.4 


93.7 
31.3 
62.4 


277.4 

13.4 

264.0 


1, 222. 1 

55.4 

1,166.7 


20.4 




8.9 






11.5 
















66.6 


95. 2 | 95. 5 


56.4 










Average food consumed per subject per dav 


1,097.9 


G07.4 


27.7 


80.5 


375.7 


6.6 



Summary of digestion ea periments with cream in a simple mixed diet. 



Experi- 
ment No. 


Subject. 


Protein. 


Fat. 


Carbo- 
hydrates. 


Ash. 


180 

181 


R. L. S 

O. E. S 


Per cent. 
70.8 
71.3 
75.8 
62.9 
43.0 
65.8 
66.6 


Per cent. 
93.2 
94.0 
92.7 
92.0 
89.3 
92.8 
95.2 


Per cent. 
97.0 
97.1 
97.3 
95.0 
93.9 
97.2 
95.5 


Per cent. 
62.8 
73. 1 


182 


R. F. T '. 


65.8 


306... 


H. F. B 


47. 6 


307 


D. G. G 


12.3 


308 

309 


R. L. S 

O. E. S 


45. 3 

56. 4 










65. 2 92. 7 96. 1 


51.9 















It is shown in the summary of the data reported above that the 
average values for the digestibility of protein, fat, and carbohydrate 
were 65.2, 92.7, and 96.1 per cent, respectively, when 28, 81, and 
376 grams of these constituents were eaten per subject daily. The 
apparent digestibility of 92.7 per cent for fat becomes 96.9 per cent 
if allowance is made for the metabolic products and fat of the basal 
ration occurring in the feces. It was anticipated that much more 
than 78 grams of milk fat or "butter" would be eaten per subject 
per day, but the subjects reported tfrat, although the blancmange 
was of better flavor and smoother texture than that to which they 
were accustomed, they did not eat as much as usual owing to its 
being ''too rich." The results of the experiments in general, how- 
ever, would indicate that butter fat supplied in the form of cream is 
very well assimilated by the body. 

EGG-YOLK FAT. 

While egg-yolk fat is not separated from eggs for use as food, it 
has an important place in the dietary, as is evident from the estimate 
that each egg supplies about 10 grams of the fat. From the results 



14 BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. 

of a large number of dietary studies, Atwater * found that over 4 per 
cent of the total fat of the diet was furnished by egg yolks. The 
digestibility of this fat is interesting on these grounds alone, but 
when it is considered that egg-yolk fat has associated with it other 
very necessary constituents of the diet, namely, the so-called •'growth- 
maintaining or stimulating factors," which have been the object of 
considerable recent investigation, it becomes of especial interest. 
Osborne and Mendel 2 and McCollum and Davis 3 have studied the 
maintenance and growth-stimulating properties of many fats and have 
found that egg-yolk fat is one of very few which are efficient in this 
respect, and it is also a fat relatively rich in lecithin. 

Although there is little experimental evidence on the subject, it 
is generally said that egg yolks are very quickly and completely 
digested. Observations and experiments on the treatment of the 
underfed led Stern 4 to conclude that egg yolks are well tolerated and 
that they may be used to supply a large proportion of the fat of the 
diet. He found that eggs left the human stomach in from one to 
one and a half hours, and that the coefficient of digestibility of the 
fat (as shown by comparison of the food and feces) was from 96.5 to 
98.5 per cent. 

These results are substantiated by the work of Levites 5 on dogs, in 
which he found that egg-yolk fat was digested in from one to four 
hours. This author concluded that egg-yolk fat behaved differently 
from other fats in the process of digestion, in that the contents 
removed from the stomach of dogs which had been given egg-yolk 
fat showed an alkaline reaction, whereas with olive oil an acid reac- 
tion was obtained. 

According to Lewkowitsch, 6 egg-yolk fat as expressed from the 
yolks of hard-boiled hen eggs is a yellow oil, while that obtained by 
ether extraction is a semisolid oil of an orange-yellow color. For 
the purpose of these experiments, however, it was not considered 
necessary to express or extract the oil, but instead it was fed as it 
occurs in the egg. The yolks were carefully separated from the 
whites, beaten, and incorporated directly in the blancmange, less 
cornstarch being required, owing to the well-known thickening 
properties of egg yolks. The blancmange made with egg yolk had 
a different consistency from that used in previous experiments, being 
more adhesive and pastelike. It also had a characteristic "eggy" 
flavor and furnished about four times as much nitrogen as the blanc- 
mange made with other fats. Five young men, living under normal 
conditions, assisted in the experiments reported on the following page. 

i Connecticut Storrs Sta. Rpt. 1899, p. 82. 
2 Jour. Biol. Chem.. 17 (1914), No. 3, p. 405. 
a Idem, 15 (1913), No. 1, pp. 107-175. 
* Med. Kec. [N. Y.], 00 (1904), No. 27, pp. 1049-1052. 
^Biochem. Ztschf., 20 (1909), No. 3-5, pp. 220-223. 

6 Chemical Technology and Analysis of Oils, Fats, and Waxes. London: Macmillan & Co., 1909,4. 
ed., vol. 2, p. 395. 



DIGESTIBILITY OF SOME ANIMAL FATS. 15 

Data of digest ion experiments tviih egg yolk in a simple mixed diet. 





Weight. 


Water. 


Pro- 
tein. 


Fat. 


Carbo- 
hydrates. 


Ash. 


Experiment No. 214, subject D. G. G.: 


Orams. 

1,826.0 
303.0 
599.0 
172.0 


Grams. 

769.7 

27.3 

520.5 


Grams. 

151.7 

32.1 

4.8 


Grams. 

267.0 

4.5 

1.2 


Grams. 

619.3 

234.2 

69.5 

172.0 


Grams. 
18.3 




4.9 




3.0 


















2,900.0 
107.0 


1,317.5 


188.6 
31.8 
156.8 


272.7 

21.8 

250.9 


1,095.0 

44.1 

1,050.9 


26.2 




9.3 






16.9 








83.1 


92.0 


96.0 


64.5 










Experiment No. 215, subject R. L. S.: 


1,669.0 
294.0 
648.0 
116.0 


703.5 
26.4 
563.1 


138.7 

31.2 

5.2 


244.0 
4.4 
1.3 


566.1 

227.3 

75.2 

116.0 


16.7 




4.7 




3.2 








2,727.0 
103.0 


1,293.0 


175.1 
32.7 
142.4 


249.7 

21.5 

228.2 


984.6 

38.4 

946.2 


24.6 




10.4 






14.2 






81.3 


91.4 


96.1 


57.7 


Experiment No. 216, subject 0. E. S.: 


1,921.0 
197.0 

1,786.0 
224.0 


809.7 

17.7 

1,552.0 


159.6 
20.9 
14.3 


280.9 
3.0 
3.6 


651.6 
152.3 
207.2 
224.0 


19.2 




3.1 




8.9 








4,128.0 
104.0 


2,379.4 


194.8 
30.9 
163.9 


287.5 

23.8 

263.7 


1,235.1 

38.5 

1,196.6 


31.2 




10.8 






20.4 




■= 




84.1 


91.7 


96.9 


65.4 


Experiment No. 217, subject R . P. T.: 

Blancmange containing egg-yolk fat' 


1,220.0 

51.0 

1,731.0 

162.0 

3,164 
62.0 


514.2 

4.6 
1,504.2 


101.4 
5.4 
13.8 


178.4 

.8 

3.5 


413.8 

39.4 

200.8 

162.0 


12.2 
0.8 


Fruit ... 


8.7 








2, 023. 


120.6 
17.4 
103.2 


182. 7 
16.4 
166.3 


816.0 
20.0 
796.0 


21.7 




8.2 






13-5 








85.6 


91.0 


97.5 


62.2 










Experiment No. 302, subject H. F. B.: 


1,316.0 

456.0 

736.0 

43.0 


507.2 
41.0 
639.6 


111. 9 

48.3 
5.9 


251.6 
6.9 
1.5 


436. 9 

352.5 

85.3 

43.0 


8.4 




7.3 


Fruit ... 


3.7 








2, 551 . 
127.0 


1,187.8 


166.1 
41.3 
124.8 


260.0 
23.7 
236.3 


917.7 
50.8 
866.9 


19.4 




11.2 






8.2 








75.1 


90.9 


94.5 


42.3 


Experiment No. 303, subject 0. E. S.: 


1,380.0 
330.0 
971.0 


531.9 
29.7 
843.8 


117.3 
35.0 

7.8 


263.8 
4.9 
1.9 


458.2 
255.1 
112.6 


8.8 




5.3 




4.9 








2,681.0 
96.0 


1, 405. 4 


160.1 
31.8 
128.3 


270.6 

21.5 

249.1 




825. 9 
33.9 
792.0 


19.0 




8.8 






10.2 








80.1 


92.1 


95.9 


53.7 


Average food consumed per subject per day 


1,008.4 


533.7 


55.9 


84.6 


326.3 


7.9 



16 BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. 

Summary of digestion experiments with egg yolk in a simple mixed diet. 



Experi- 
ment No. 


Subject. 


Protein. 


Fat. 


Carbohy- 
drates. 


Ash. 


214 


D. G. G 


Per cent. 
83.1 
81.3 
84.1 
85.6 
75.1 
80.1 


Per cent. 
92.0 
91.4 
91.7 
91.0 
90.9 
92.1 


Per cent. 
96.0 
96.1 
96.9 
97.5 
94.5 
95.9 


Per cent. 
64.5 


215 

216 

217 


K.L. S 

O.E.S 

R. F. T 


57.7 
65.4 
62.2 


302 

303. . 


H. F. B 

0. E. S 


42.3 
53.7 










81.6 


91.5 


96.2 


57.6 









It may be noted from the recorded data of these experiments that 
the average amounts of protein, fat, and carbohydrate eaten daily 
were 56, 85, and 326 grams, of which 81.6, 91.5, and 96.2 per cent 
were digested, respectively. The reported digestibility of 91.5 per 
cent for the total fat of the diet is increased to 93.8 per cent for the egg- 
yolk fat by making allowance for metabolic products and any undi- 
gested portion of the small amount of fat the basal ration supplied. 
Inasmuch as the egg-yolk fat comprised 98 per cent of all the fat 
supplied by the diet, this derived value should very closely approxi- 
mate the true digestibility of egg-yolk fat. 

In the course of the analytical work it was observed that the ether 
extracts of both the blancmange and the feces of the experimental 
periods were of a very dark-orange color, somewhat more intense in 
the case of the feces. This discoloration can probably be attributed 
to coloring matter extracted from the egg yolk. 

FISH FAT. 

Though fish fat or oil (for it is liquid at ordinary room temperature) 
is not a culinary or table fat in our temperate regions, nevertheless, 
as it occurs in fish flesh, it forms a not inconsiderable part of the total 
fat of the diet. This is particularly the case in localities where such 
fish as mackerel, butterfish, salmon, shad, etc., are eaten in quantity. 
Except in the case of cod-liver oil, which is a special product used in 
invalid dietetics chiefly because of the medicinal properties attributed 
to it, experimental studies of food uses of fish fat or oil are apparently 
few in number. 

Atwater, 1 in a study of haddock compared with beef, reports that 
the fish fat was 91 per cent digested. Some years later Milner, 2 in 
experiments with four young men, found that the digestibility of the 
fat of a lean fish (cod) was practically the same as that of a fat fish 
(canned salmon), the values "being 97.4 per cent and 97 per cent, 
respectively. 

Since fish oil suitable for food purposes was not found on the market 
and it was not practicable to prepare it in the laboratory, fish con- 
taining a fairly high percentage of fat was used instead in the experi- 

i Ztschr. Biol., 24 (1SS8), pp. 16-2S. 

2 Connecticut Storrs Sta. Rpt. 1905, pp. 116-142. 



DIGESTIBILITY OF SOME ANIMAL FATS. 



17 



merits here reported. For convenience it was served in the form of a 
fish loaf rather than incorporated in a cornstarch blancmange, such 
as was used with the other fats. With the fish loaf a simple basal 
ration was served which consisted of potato (boiled and mashed) and 
biscuits or crackers, fruit (raw apples), and sugar with tea or coffee 
when such beverages were preferred to water. A small amount of 
lemon juice was used with the fish as a condiment, but no account 
was taken of it in computing the nutritive value of the ration. 

The fish loaf was prepared as follows: Boston mackerel (a typical 
fat fish), weighing when cleaned approximately 3 pounds each, were 
washed and cooked in a covered pan for half an hour in a moderate 
oven, a little water being added so that the fish would not stick to the 
pan. The bones, skin, etc., were then removed and the fish flesh 
minced in an ordinary household meat cutter. The small amount of 
liquid which remained in the pan was mixed with the minced fish 
to avoid the loss of any fat which had "cooked out." After season- 
ing moderately with salt and pepper, the minced fish was formed into 
a loaf and baked two or three hours in a moderate oven. The crusty 
surface was removed and the inside portion of the loaf was thoroughly 
mixed and divided into suitable quantities for the subjects' meals. 

Though different in form, the diet was similar in nutritive value to 
those in the other experiments here reported, fish protein replacing 
the protein of the skim milk used in making the cornstarch blanc- 
mange and mashed potato replacing the cornstarch. That the diets 
were directly comparable in nutritive value is evident from a com- 
parison of the protein, fat, and energy which the subjects obtained 
per day from each. 

The details of the three experiments which were made follow. 

Data of digestion experiments with Boston mackerel in a simple mixed '//'< /. 





Weight. 


Water. 


Pro- 
tein. 


Fat. 


Carbo- 
hydrates. 


Ash. 


Experiment No. 444. subject D. <;. G.: 

Boston mackerel (in form of fish loaf) 


Grams. 

1, 496. 
439.0 
284.0 

1, 320. 
171.0 


Grams. 

926.0 

331.5 

19.6 

1,116.7 


Grams. 

323.0 

11.0 

23.0 

5.3 


Grams. 

199. 9 

.4 

3S.0 

6.6 


Grams. 


Grams. 
47.1 


91.7 
201.1 
187.4 
171.0 


4.4 




2.3 


Fruit 

Sugar 


4.0 












3,710.0 
67.0 


2, 393. 8 


362.3 

19.3 

343.0 


244.9 
10.1 

234. S 


651.2 
31.9 
619.3 


57.8 




5.7 






52.1 
















94.7 


95.9 


95.1 


90.1 










Experiment No. 446, subject R. L. S.: 

Boston mackerel (in form of fish loaf) 


1,184.0 
227.0 
243.0 

1,376.0 
58.0 


732.9 

171.4 

16.8 

1,164.1 


255. 6 
5.7 
19.7 
5.5 


158.2 
.2 

32. 6 
6.9 




37.3 


47.4 
172.0 
195. 4 

58.0 


2.3 




1.9 


Fruit 


4.1 


















3,088.0 
53.0 


2, 085. 2 


280.5 
21.9 

264. 6 


197.9 
190! 4 


472.8 
16. 2 

456. 6 


45.6 




7.4 






38.2 
















92.4 


96.2 


96. 6 


83.8 












18 BULLETIN 507,, U. S. DEPARTMENT OF AGRICULTURE. 

Data of digestion experiments with Boston mackerel in a simple mixed diet — Continued. 





Weight. 


Water. 


Pro- 
tein. 


Fat. 


Carbo- 
hydrates. 


Ash. 


Experiment No. 447, subject 0. E. S.: 

Boston mackerel (in form of fish loaf) 


Grams. 

1, 348. 
476.0 
171.0 

1,594.0 
165.0 


Grams. 

834.4 

359.4 

11.8 

1, 348. 5 


Grams. 

291.0 

11.9 

13.8 

6.4 


Grams. 

180.1 

.5 

22.9 

8.0 


Grams. 


Grams. 
42.5 


99.5 
121.1 
226.3 
165.0 


4.7 




1.4 


Fruit 


4.8 


















3. 754. 
70.0 


2, 554. 1 


323.1 

28.6 

294.5 


211.5 

12.2 

199.3 


611.9 

21.6 

590.3 


53.4 




7.6 






45.8 
















91.1 


94.2 


96.5 


85.8 










Average food consumed per subject per day 


1, 172. 5 


781.5 


108.0 


72.7 


192.9 


17.4 



Summary of digestion experiments — Digestibility of nutrients of entire diet. 



Experi- 
ment No. 


Subject. 


Protein. 


Fat. 


Carbohy- 
drates. 


Ash. 


444 

446 

447 


D. G. G 

R. L. S 

O.E. S 


Per cent. 
94.7 
92.4 
91.1 


Per cent. 
95.9 

96. 2 
94.2 


Per cent. 
95.1 
96.6 
96.5 


Per cent. 
90.1 
83.8 
85.8 




92.7 


95.4 


96.1 


86.6 









As the tables show, the experimental diet supplied, on an average, 
108 grams protein, 73 grams fat, and 193 grams carbohydrates per day. 
The coefficients of digestibility of the entire diet were: Protein, 92.7 
per cent; fat, 95.4 per cent; and carbohydrates, 96.1 percent. 

The amount of fat supplied by other foods than fish was only 17.7 
per cent of the total fat of the diet. Making due allowance for this 
small amount of fat other than fish fat made no significant change, the 
corrected value being 95.2 per cent as compared with 95.4 per cent. 
This is comparable with the values obtained for other fats of similar 
physical characteristics and indicates that, like them, fish fat is well 
assimilated. 

SUMMARY. 

The fats studied in this investigation were well digested, the coeffi- 
cients of digestibility, with allowance for metabolic products and any 
undigested fat supplied by the basal ration, being, for chicken fat, 
96.7 per cent; for goose fat, 95.2 per cent; for brisket fat, 97.4 per 
cent; for butter fat in the form of cream, 96.9 percent; for the fat in 
egg yolk, 93.8 per cent; and for the fat in fish flesh, 95.2 per cent. 

On an average, 95 grams of chicken fat, 95 grams of goose fat, 80 
grams of brisket fat, 78 grams of butter fat in the form of cream, 83 
grams of egg-yolk fat, and 60 grams of fish fat were eaten per subject 
per day. In the case of goose fat, the feces were noticeably soft and 
occasionally a more decided laxative effect was noted, indicating that 
the limit of tolerance for this fat was not far above the 95 grams 



DIGESTIBILITY OF SOME ANIMAL FATS. 19 

which was eaten on an average. No physiological disturbance was 
noted with the other fats tested. Such matters have a practical 
value in discussing dietetics, aside from the theoretical question 
whether this laxative property is ascribable to differences in the 
chemical structure of the fats or to some other factor. 

The average coefficient of digestibility of brisket fat is higher than 
that previously found for beef (kidney) fat (93 percent), 1 which is in 
accordance with the observation that the digestibility is inversely 
proportional to the melting point. The other fats studied were either 
fluid or had a melting point not far from room temperature, so it was 
not surprising to find that they did not show marked variations in 
thoroughness of digestion. 

The average digestibility of carbohydrates in the different tests was 
found to vary only from 96.1 to 96.9 per cent, while the digestibility 
of this food constituent in the average mixed diet has been found to 
be 97 per cent. 2 This close agreement would indicate that the con- 
sumption of fat did not exercise any unusual effect upon carbohydrate 
digestion. 

As a whole, the results of the digestion experiments indicate that 
chicken fat, goose fat, brisket fat, cream, egg-yolk fat, and fish fat 
are all well assimilated and that they are satisfactory sources of fat 
for the dietary. Since butter fat eaten in the form of cream and 
egg-yolk fat are very thoroughly digested and easily obtainable and 
apparently contain or carry with them accessory food substances 
necessary in the diet for growth and general well-being, a wide use of 
these two fats in the dietary is especially desirable. 

i U. S. Dept. Agr. Bui. 310, p. 21. 

2 Connecticut Storrs Sta. Rpt. lUOl, p. 245. 



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